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    Effect of new design of elongated jet hole on thermal efficiency of solar air heater
    (Elsevier, 2022) Pazarlioglu, Hayati Kadir; Tepe, Ahmet Umit; Tekir, Mutlu; Arslan, Kamil
    Effect of new design of elongated jet hole on the thermal efficiency (eta th) of a solar air heater (SAH) has been numerically studied in this paper. Jet impingement technique, which is one of the important active techniques, has been implemented on the absorber plate of the SAH surface to increase the convective heat transfer per-formance. Several designs of elongated jet hole (EJH) technique (gradually increasing, gradually decreasing along the crossflow direction, and equally extended), which is highly effective application to get rid of cross-flow, has been inserted to the jet plate. The main interest of this paper is to investigate the effect of different EJH configurations on convective heat transfer performance and eta th of the SAH. 15 x 7 array of jets have been mounted on the confinement plate. Results have been compared with the conventional SAH, which has the jet impingement Case1. Numerical computations have been conducted using RNG k -epsilon turbulence model. Average Nusselt number (Nu) on the absorber plate surface, eta th of the SAH, and performance evaluation criteria (PEC) have been quantitatively investigated comprehensively. As a result of calculations, the Nu and eta th of SAH can be enhanced by 31.80 % and 2.46 %, respectively, using Case4 instead of Case1 at Re = 25000. Besides, the pressure drop of SAH dramatically rises by 10.26 %, when Case4 and Case1 compared with each other at Re = 25000. Despite increment in pressure drop, the PEC value achieves to 1.28. Finally, it is concluded that the equally extended EJH presents well performance compared to gradually increasing and decreasing EJH.
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    Effects of Extended Jet Holes to Heat Transfer and Flow Characteristics of the Jet Impingement Cooling
    (Asme, 2019) Tepe, Ahmet Umit; Arslan, Kamil; Yetisken, Yasar; Uysal, Unal
    In this study, effects of extended jet holes to heat transfer and flow characteristics of jet impingement cooling were numerically investigated. Cross-flow in the impinging jet cooling adversely affects the heat transfer on the target surface. The main purpose of this study is to reduce the negative effect of cross-flow on heat transfer by extending jet holes toward the target surface with nozzles. This study has been conducted under turbulent flow condition (15,000 <= Re <= 45,000). The surface of the turbine blade, which is the target surface, has been modeled as a flat plate. The effect of the ribs, placed on the target surface, on the heat transfer has been also investigated, and the results were compared with the flat surface. The parameters such as average and local Nusselt numbers on the target surface, flow characteristics, and compressor power have been examined in detail. It was obtained from the numerical results that the average Nusselt number increases with decreasing the gap between the target surface and the nozzle. In addition, the higher average Nusselt number was obtained on the flat surface than the ribbed surface. The lowest compressor power was achieved in the 5Dj nozzle gap for the flat surface and in the 4Dj nozzle gap for the ribbed surface.
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    Experimental and numerical investigation of jet impingement cooling using extended jet holes
    (Pergamon-Elsevier Science Ltd, 2020) Tepe, Ahmet Umit; Yetisken, Yasar; Uysal, Unal; Arslan, Kamil
    In this study, jet impingement cooling on flat surface was investigated experimentally. The aim of this study is to elucidate the effect of extended jet holes on the heat transfer performance of the in-line array jet impingement configuration. The studies were performed under fully turbulent flow condition (16250 <= Re <= 32500). Local Nusselt number (Nu) distribution on the surface of interest was obtained experimentally by using Transient Liquid Crystals (TLC) method. Numerical investigations were conducted as the same configuration with the experimental method to explore the flow and heat transfer characteristics. SST k-omega with low-Re correction turbulence model was used for solving turbulence equations. Experimental and numerical studies were conducted on 1 x 6 (in-line array) jet impingement cooling configuration. Dimensionless jet to jet spacing (X-n/D-j), dimensionless jet plate to target plate spacing (Z/D-j) and dimensionless target plate width (Y/D-j) were taken as 5.0, 6.0 and 6.0, respectively. Five different G(j)/D-j= (1.0, 2.0, 3.0, 4.0 and 5.0) were investigated and the results were compared with orifice plate jet impingement configuration (Z/D-j=G(j)/D-j=6.0). Average and local Nu number distributions, pressure drop of the system, flow characteristics and Performance Evaluation Criterion (PEC) were examined in detail. Numerical results were compared with the experimental data and it was obtained that SST k-omega turbulence model was able to accurately predict the average and local Nu number distributions on the surface of interest. The maximum average and local Nu numbers were obtained on the condition of G(j)/D-j=2.0. Furthermore, PEC shows that the most feasible dimensionless nozzle to target plate gap was G(j)/D-j=2.0 at all Re numbers. (C) 2020 Elsevier Ltd. All rights reserved.
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    Jet impingement cooling on a rib-roughened surface using extended jet holes
    (Pergamon-Elsevier Science Ltd, 2020) Tepe, Ahmet Umit; Uysal, Unal; Yetisken, Yasar; Arslan, Kamil
    In this study, jet impingement cooling on a rib-roughened surface has been investigated experimentally. The aim of this study is to investigate the effect of extended jet holes on the heat transfer performance and flow characteristics of the jet impingement cooling on a rib-roughened surface. The studies have been conducted under turbulent flow condition (16,250 <= Re-j <= 32,500). Transient Liquid Crystals (TLC) method has been employed to investigate the average and local Nusselt number (Nu) distributions on the surface of interest. Six inline arrays of jet impingement configuration have been examined as the jet impingement cooling system. Jet holes were extended towards the target surface with the nozzles. Various dimensionless nozzles to the target surface gaps (G(j)/D-j = 1.0, 2.0, 3.0, 4.0 and 5.0) have been investigated. Rectangular cross-sectional ribs were located on the surface of interest for the augmentation of heat transfer. Experimental studies were conducted on the dimensionless rib height as H-r/D-j = 0.42. In addition, numerical studies were carried out to investigate the flow and heat transfer characteristics. The effect of various dimensionless rib heights (H-r/D-j) on convective heat transfer performance has also been investigated numerically. SST k-omega with low-Re correction turbulence model was used for solving turbulence equations. Average and local Nu number distributions, flow characteristics and Performance Evaluation Criterion (PEC) were examined in detail. Results were compared with the orifice plate (G(j)/D-j = 6.0) jet impingement configuration. Results showed that SST k-omega turbulence model accurately reveals the experimental data. Application of extended jet holes is a feasible method for practical application of the jet impingement cooling, especially at relatively low dimensionless nozzle gap (G(j)/D-j <= 4.0). Furthermore, improperly designed rib height has been found to diminish heat transfer performance.
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    Thermohydraulic performance assessment of new alternative methods for anti-icing application against current application in an aircraft
    (Sage Publications Ltd, 2023) Pazarlioglu, Hayati Kadir; Tepe, Ahmet Umit; Arslan, Kamil
    In this study, anti-icing problems, which are mostly industrial problems in aerospace companies, have been numerically investigated. Herein, to enhance anti-icing performance of NACA0015, different jet-to-surface distances (H/d), jet angles (& alpha;), and slot jet designs with different aspect ratios (ARs) have also been investigated. ANSYS Fluent 2020R2 commercial program has been utilized for all numerical calculations. In addition, the SST k-& omega; with low-Re correction wall treatment turbulence model has been used for solving turbulence equation. Furthermore, the average Nusselt number (Nu) on the NACA0015's surface, pressure drop, and performance evaluation criteria (PEC) which define the anti-icing performance of novel proposed system have been presented section by section. As a result of the investigation, it has been obtained that the use of AR = 4 increases the Nu by 85.52% compared to circular jet for the H/d = 4 at & alpha; = 90 & DEG;. The pressure drop value dramatically increases using AR = 4 around 307.85% compared to circular jet for H/d = 4 at & alpha; = 90 & DEG;. Despite this drastic increment in pressure drop, the PEC value is kept as 1.14 using AR = 4, H/d = 4, and & alpha; = 90 & DEG;. Finally, empirical correlations developed from existing findings have been presented with an error rate of lower than 5%.